This invention relates to the production of metal strips and, more particularly, to opening apparatus having an alignment system used in the production of metal strips from split tubes. The resultant strips are particularly suitable for use in the coils of power transformers.
Power transformers, such as overhead distribution transformers and pad mounted distribution transformers, generally include coils which are wound from relatively wide strips of aluminum. In order to provide the requisite electrical characteristics for such transformers, it is necessary that the aluminum strips not only have accurate dimensions, but also have other desired characteristics, such as a desired electrical conductivity and 0-temper.
Heretofore, the aluminum strips have been produced by first casting aluminum into ingots and then cold rolling and hot rolling the ingots to form sheets which are then slit to form the strips. In addition, the strips have been subjected to secondary metal treating processes to contour or curve the edges thereof. Contoured edges enable the strips to be insulated with a dielectric in an optimal manner.
While the foregoing processing has produced satisfactory strips, because of the number of steps involved, it is relatively costly. Accordingly, a continuous process minimizing the number of discreet steps is desirable. In this connection, consideration has been given to conventional extrusion processes. However, such conventional extrusion does not permit the continuous processing that is desired in connection with the production of flat metal strips for power transformer coils.
Accordingly, the above-noted parent application provides a new and improved method and apparatus, employing continuous extrusion, to continuously form flat metal strips suitable for producing coils for power transformers. More specifically, in accordance with the invention of the parent application, first and second continuous rod-like billets are fed through first and second circular grooves formed respectively in a rotating wheel. The first and second billets are advanced by the rotating wheel through a passageway formed between the wheel and a stationary shoe. The billets are advanced by the rotating wheel to first and second abutments positioned to enter the first and second grooves, respectively. The abutments block movement of the billets through the passageway, the billets thereby being plastically deformed and forced out of the grooves to an opening in a die positioned adjacent to the wheel. The deformed first and second billets merge within the die opening which has a circumferentially discontinuous, annular cross sectional shape, and exit therefrom in the form of a slit tube. The tube is then advanced to a forming station at which the tube is opened and flattened by bending it outwardly in opposite directions at the slit.
In accordance with an aspect of the invention of the parent application, an elongated forming member and an opposing surface are provided for opening and flattening the tube. The elongated forming member has an entrance end and an exit end. The entrance end has a width equal to or less than the diameter of the tube, the width progressively increasing from the entrance end toward the exit end of the forming member. Preferably, the opposing surface is flat and in a preferred embodiment is a flat moving belt. The tube is advanced over the forming member and against the flat surface such that the forming member opens the tube from the slit outwardly and forms the tube into a substantially flat strip.
It is highly desirable when opening the tube into a flat strip, as described above, that the tube be centered in the opener as it is pulled therethrough. On occasion, the tube will tend to twist as it is being extruded. If it does, or if it is twisted or off-center when it is inserted into the opener, or if for some other reason misalignment occurs while in the opener, the tube will move off to the side and possibly even out of the opener, causing damage to the edges of the tube or resultant flat strip. It is, therefore, important that alignment of the tube with the opener as it is pulled through the opener be maintained.
One way to accomplish this would be to use guide fingers, pads or rollers on the two surfaces and/or edges to maintain alignment. These, however, would be difficult to thread through the opener and other component parts of the system, could damage the tube's surfaces that they make contact with and would also need to be repositioned when the tube circumference or, correspondingly, the width of the strip changes.